1. Field of the Invention
The present invention relates to the effective leak detection in heating, ventilating and air conditioning systems and more particularly to such systems which utilize hydrofluorocarbon (HFC) refrigerants, by the addition of optical brighteners.
2. Background Art
Because of the damage that Freon.RTM. (CFC) refrigerants are doing to the ozone layer, it has become necessary for the development of alternative refrigerants which are environmentally friendly. DuPont, International Chemicals and others have developed HFC refrigerants, which are much safer in the environment and have an ozone depletion factor of 1, rather than an ozone depletion factor of 8, as is found for Freon refrigerants. The use of these new refrigerants has rendered prior leak detection systems employing materials such as those described in U.S. Pat. Nos. 4,758,366 and 5,149,453, both issued to Manher Parekh on Jul. 19, 1988 and Sep. 26, 1992, respectively, as ineffective. These patents teach yellow fluorescent dye dissolved with mineral oils which are hydrocarbons and therefore poorly soluble in the new polyalkylene glycol and polyol ester lubricants which are being used in the new HFC refrigerant containing systems. For this reason, the hydrocarbon soluble dyes described in the above referenced patents are not suitable for use in heating, ventilating and air conditioning systems employing the new HFC refrigerants.
The non-polar nature of the dyes disclosed by Parekh render them unsuitable for use in highly polar alcohol type refrigeration lubricants such as polyalkylene glycols. For this reason, the hydrocarbon soluble dyes described by Parekh are not suitable for use in the new HFC (Suva from DuPont) refrigerants.
The new HFC systems reach higher operating temperatures than the old CFC systems because of different thermodynamic properties. Typical operating temperatures of the new HFC refrigerant systems reach temperatures in excess of 420 degrees Fahrenheit while the old CFC systems reached temperatures of 300 degrees Fahrenheit. It is claimed by Parekh that the perylene fluorescent dyes are stable up to 400 degrees Fahrenheit. The temperature stability of the perylene dyes is actually much lower, about 250 degrees Fahrenheit.
This problem of poor temperature stability is clue to the highly delocalized electronic configuration of the perylene molecule. This delocalization of electrons is actually what gives the perylene molecule its fluroescence. When the perylene dye is exposed to 365 nanometer wavelength ultraviolet light, electrons are excited and jump to a higher energy level. This excitation happens only briefly and then the electrons fall back to their original energy level and emit photons of a specific wavelength which in this case is the wavelength for yellow light. When the perylene molecule is exposed to high temperatures, its electronic configuration is scattered and later permanently destroyed rendering it a non-fluorescent molecule and therefore ineffective at locating leaks. The perylene dyes described by Parekh were used to find leaks in oils and in systems which contain a hydrocarbon based fluid (which all refrigeration lubricants used in CFC containing systems are) to enable the user to find leaks. The perylene dyes claimed by Parekh have been used for over 60 years to find leaks in mineral based systems which are not exposed to high operating temperatures. Perylene dyes are therefore a poor choice for leak detection in systems which are exposed to elevated temperatures such as refrigeration systems which contain the new HFC refrigerant manufactured by DuPont called Suva. The perylene dyes described by Parekh work poorly in the elevated temperatures of the CFC containing systems and even worse in the new HFC containing systems where the operating temperatures are much higher, up to 420 degrees Fahrenheit. For these reasons, a new fluorescent dye composition is required for the HFC systems which use a new type of polar refrigeration lubricant and have very high operating temperatures.
For example, an automobile air conditioning system was charged with R-134a (DuPont). Approximately 0.1 grams of perylene fluorescent dye (FC-131 Morton Chemical) was added to 7.75 ounces of a polyalkylene glycol refrigerant lubricant and then scanned with an ultraviolet light. A bright yellow fluorescence was observed. The system was charged with the dye-lubricant mixture and then operated. A temperature gauge was attached to the evaporator core so that an accurate operating temperature could be measured. A valve was placed on a hose so that some refrigerant/oil could be released and then observed when an ultraviolet lamp was used. Table I shows the results obtained.
TABLE I ______________________________________ Operating Time Operating Temp Fluorescence of (Minutes) (degrees F.) Dye/Refrig./Oil ______________________________________ 2 110 Excellent 5 230 Good 7 250 Weak 10 290 None 12 310 None 15 380 None ______________________________________